In our copending applications Ser. No. 149,065 filed May 12, 1980 for an Electro-Hydraulic Proportional Actuator and Ser. No. 166,731 filed July 7, 1980 for an Electrically Operated Hydraulic Power Lift System, now U.S. Pat. No. 4,343,365, we noted that agricultural tractor controls traditionally have been a hydro-mechanical system wherein, for example, implement draft is sensed mechanically. Through appropriate mechanical linkage, a hydraulic valve is actuated to supply operating fluid to a hydraulic cylinder for raising and lowering the implement.
The development of low-cost, reliable electronic microcomputers has introduced an unlimited flexibility in the design of tractor control systems. The primary requirement for implementing any tractor electro-hydraulic system is a low-cost, contaminant insensitive, environmentally sound interface device, preferably a hydraulic proportional actuator, such as is disclosed in our aforementioned application Ser. No. 149,065, for converting an electric signal to either a mechanical or hydraulic output device.
Operation of a hydraulic proportional actuator to control, for example, a hydraulic remote valve, requires a compatible control system such as is provided by the present invention.